This invention relates to a dump valve provided with a closure piston plug and an inner cylindrical guide member therefor.
Various types of air dump valves are known in which a closure piston plug alternately closes a dump aperture during feeding of compressed air into a storage tank and a feed aperture during dumping of the stored air from the tank toward a user structure.
Such valves have a multiplicity of applications. For example, they are used for dumping a tank or can be applied to an air ram to improve its speed of operation or finally they find an interesting application as compressed air guns for opening clogged silos, hoppers and ducts containing granular or powdery materials.
European Patent Application No. 134,726, filed June 7, 1984 and published Mar. 20, 1985, discloses an air dump valve in which a piston is guided for axial movement by a short peripheral flange engaging with ample clearance a cylindrical valve body.
Valves of this type may give rise to some drawbacks. For example, when they are mounted in the vicinity of a source of heat or when they are incidentally overheated by heat coming from the user structure, the piston may dilate until it grips by contact with the surrounding walls of the valve body. Also the very presense of clearance between the piston and the valve body may lead to a misaligned movement and a tendency of gripping. Further, in case of gripping, the replacement of the piston usually necessitates dismounting of the valve from the user structure, which is always disagreeable. Finally, it is to be noted that the provision of a relatively short piston mounted with clearance relative to the valve body may permit impurities or dust coming from the dump aperture to penetrate into the valve body by the return effect.
It is an object of the present invention to eliminate or reduce the aforementioned drawbacks by providing a dump valve that will afford greater security against gripping by thermal effects on the piston, is provided with guide means for the piston to prevent gripping by misalignment and, in case of gripping, will permit removal of the piston without having to dismount the valve from the user structure.
It is a further object of the present invention to provide a dump valve that can be used in plants or structures involving the user of granular or powdery materials, substantially without causing the return of such materials into the valve body.